Equine Health Update EHU Vol 19 Issue 3 - Page 19

EQUINE | Equine Disease Update of epidemiological studies and pedigree analyses to find common factors among cases. Hydrocephalus, for example, is a developmental disor- der that often results in stillbirth of foals and dystocia in dams. Possible causes of the defect in horses could not be proven based on field data and pedigree analy- ses suggested the disorder to be complex. With this in mind, a genome scan of 82 horses (13 cases, 69 controls) was performed and a small section of the genome was identified as containing the cause of the disorder. Ge- nomic sequencing was then performed on 10 horses (4 cases, 6 controls) and the genetic cause of the disorder was pinpointed. Ultimately, 2 copies of a mutation that changed a “C” nucleotide to a “T” nucleotide (Figure 1) resulted in the disorder. Although previously believed to be a complex dis¬ease, genetic and genomic methods were able to prove that the disorder was in fact simple, leading to the develop- ment of a genetic test that can help breeders avoid the disorder. It is important to note the difference between a genetic test for a simple disease, such as hydrocephalus, and a genetic test for a complex disease (e.g. osteochon- drosis). Genetic tests for simple diseases can confirm or rule out a genetic condition; however, genetic tests for complex diseases only help to determine an individual’s chance of developing a genetic disorder—an important dis¬tinction when genetic tests are used to help make breeding decisions. pro¬vide an opportunity to cross certain disorders off that list, thereby helping to eliminate or reduce the oc- currence of those diseases. Contact: Dr. Brandon D. Velie brandon.velie@slu.se Department of Animal Breeding & Genetics Swedish University of Agricultural Sciences Uppsala, Sweden International Horse Movements and Disease Risk The World Organization for Animal Health (OIE) is re- sponsible ior ensuring transparency of the global animal disease situation by requiring reporting of occurrences of animal diseases of eco¬nomic and public health im- portance by its member countries as well as safeguard- ing the health and safe trade of animals and animal products by setting international standards document- ed in the OIE Terrestrial Animal Health Code (TAHC). Incidents of disease introduction associated with in- ternational movement of live horses are sporadical¬ly reported to the OIE for immediate notification via the OIE World Animal Health Information System (WAHIS). From 1995 to 2014, 54 incidents were reported to the OIE. The immediate notification reports from the Mem- ber Countries were reviewed in conjunction with other information available in the public domain to provide the following analysis. In either scenario, genetics and genomics in Thorough- breds have far-reaching potential beyond that of breed- ing and selecting faster horses. Understanding diseases caused by a single gene as well as complex dis¬eases caused by multiple genes and the environment can lead to early diagnosis and targeted treatments. Equine influenza (13 events) and contagious equine metritis (12 events) were the most fre¬quently report- ed diseases. For seven events, the infected horses were de-tected during post-arrival quarantine and were not released into importing countries. The 47 other events resulted in the introduction of pathogens into import- ing-countries. While the list of reasons a racehorse never reaches its potential may seem endless, genetics and genomics Subclinical infections remain a challenge for interna- tional trade. In 88 percent of reported events, infected • Volume 19 no 3 • September 2017 • 19